Radio receiver



April 20, 1937. w. D. LOUGHLIN RADIO RECEIVER Filed Dec. 11, 1953 2Sheets-Sheet l (1cm M41146.

W. D. LOUGHLIN RADIO RECEIVER April 20, 1937.

Filed Dec. ll, 1953 2 Sheets-Sheet 2 Patented Apr. 20, 1937 UNITEDSTATES PATENT OFFICE RADIO RECEIVER ration of Delaware ApplicationDecember 11, 1933, Serial No. 701,917

18 Claims.

This invention relates to radio receivers and particularly to receiverswhich include elements operable automatically to suppress all noise anddisturbing output when the receiver is not tuned 5 to some one of aplurality of pre-selected stations.

Receivers of this type are described and claimed in my copendingapplication Serial No. 691,541, filed September 29, 1933, and include,in general, circuit elements for normally suppressing the 1; receiveroutput, either partially or completely,

and a muting switch system operable synchronously with the tuningadjustment for restoring normal operation when the receiver is tuned toone of the selected stations. The switch system 15 preferably includesindexing elements which facilitate the tuning to desired stations byyieldingly arresting the tuning control as it reaches a positioncorresponding to a selected station, and

a manually operated switch for rendering the automatic muting systeminoperative when it is desired to tune the receiver in the usual mannerto any station within the entire operating range.

An object of the present invention is to provide a radio receiverincluding a simple and efficient 25 muting switch system. An object isto provide a muting switch system which is not associated with thetuning dial of the receiver and which therefore imposes no materialrestrictions upon the design of the receiver chassis, cabinet or dialmember. A further object is to provide a receiver including a mutingsystem having a relatively large space for the location of theadjustable elements which determine the pre-selected frequencies thatmay be received. A further object 5 is to provide a receiver including amuting system having elements affording an index for facilitating tuningwhen the muting system is adjusted to receive only the selected favoritestations, and apparatus for rendering the indexing system inoperativewhen the muting system is adjusted to permit tuning to any stationwithin the operating range of the receiver.

These and other objects and advantages of the invention will be apparentfrom the following specification when taken with the accompanyingdrawings, in which,

Fig. 1 is a fragmentary circuit diagram of a radio receiver embodyingthe invention,

Figs. 2 and 3 are an end elevation and a fragmentary side view,respectively, of a muting switch system mounted on the end of a gangcondenser,

Fig. 4 is a side elevation of the switch struc- 55' lure Figs. 5 and 6are fragmentary sections taken on lines 55 and 6-6, respectively, ofFig. 2,

Figs. 7 and 8 are enlarged fragmentary sectional views showingalternative adjustments of the switch structure,

Fig. 9 is a fragmentary perspective view of another form of cam andfixed contact plate, and

Figs. 10 to 12 are perspective views illustrating other forms of contactfingers.

The general circuit arrangement and method of operation are indicated inthe fragmentary and schematic circuit diagram of a radio receiver, Fig.l. The receiver may be of any convenient or preferred design and willusually include one or more radio amplifier tubes l havingtuned inputcircuits each comprising an inductance 2 and tuning condenser 3. Thetube or tubes I work into succeeding stages, indicated schematically bythe block 4, which include a detector and an audio amplifying systemworking into a reproducer 5. The succeeding stages may include a tunedcircuit, as indicated by the condenser 6, such as a further radiocircuit or the local oscillator circuit, and all tuning elements arepreferably mechanically connected, as indicated by the broken line I, toa common shaft 8 that carries or is connected to a tuning knob 9.

In accordance with the invention, a muting switch is mounted on oractuated synchronously with the shaft 8 to control the operation of thereceiver. The exact form and location of the muting circuits in whichthe switch is located are subject to variation to meet different designrequirements and, as shown in Fig. 1, the muting system includes abiasing resistor I!) in series with the normal cathode bias resistancell of the tube or tubes I, the resistor It being by-passed to ground forradio frequencies by a condenser I2. The muting switch includes a fixedcontact l3 connected to the cathode terminal of the resistor 80, and aplurality of contact fingers 14 that are mounted on the shaft 8 andconnected to ground. The resistor It is of such value as to develop aheavy bias voltage which blocks or substantially suppresses transmissionby the tube or tubes 1 to extinguish or to materially reduce the outputof the reproducer 5 when the tuning shaft is so adjusted that the mutingswitch l3, I4 is open. When the receiver is tuned to a pre-selectedstation corresponding to the engagement of a contact finger [4 with thefixed contact 13, the resistor I is short circuited and normaltransmission takes place since the bias voltage developed by theresistor II is appropriate for high amplification. A manually operatedswitch I is preferably connected across resistor III to permit normaltransmission throughout the entire tuning range when the switch isclosed.

As shown in Fig. 2, the switch mechanism is mounted upon a plate I6which may be, and conveniently is, the end plate of a gang condenserassembly which has a plurality of movable plate sections mounted on arotor shaft 8. This mounting of the switch mechanism has the advantagethat there is no backlash or lost motion between the tuning condenserand the movable switch members. A pair of contacts I3 are mounted uponthe opposite fianged ends of an elongated plate I! which has itsapertured center portion in contact with the projecting hub of anannular disk I8, the disk and the plate I! being both fixed to the plateI6 by screws I9 which are threaded into the plate I6. The plate I1 isresilient and the outer ends of the plate may be forced away from thefixed plate I6 by the cam flanges 20 on a cam plate 2| which isrotatably mounted on the hub of the disk I8, the cam plate beingangularly adjustable by a shaft 22 and linkage 23.

As shown in Figs. 7 and 8, insulating strips 24 are provided between thecontacts I3 and the plate I1, and the contacts have lugs I5 which extendtoward the plate IE to serve as the movable contacts of a pair ofparallel switches. In the usual receiver design, the condenser framewill be grounded on the chassis and the insulated contacts I3 may beconnected to the junction of the biasing resistors II), II by leads 24a.Each contact element I3, I5 therefore combines the contacts I3 and I5 ofthe Fig. 1 circuit into a single element that is manually displaceable,as will be explained later, from position in engagement with the fixedcontact or plate I6 into a position in the path of movement of themovable contacts of the muting switch system. Normal transmissionthrough the receiver is possible only when the contact element I3, I5engages either the fixed contact I6 or one of the contacts I4.

The several contact fingers I4 are adjustably mounted on a disk 25 whichis secured to the projecting end of the rotor shaft 8, the parts preferably having mating non-circular portions to prevent relative rotationof the disk and shaft. The hubs of the contact fingers I4 have circularopenings to permit their angular adjustment on the shaft 8, and thefingers are clamped in desired positions by screws which pass throughthe fingers and engage nuts 26 that have flattened portions extendinginto the arcuate slots 21 of the disk 25. The slots 21 have an angularextent of almost 360 and therefore provide a correspondingly wide rangeof adjustment for the contact fingers. Although the range of adjustmentof the tuning condenser is usually about the fingers I4 may bepositioned over twice that range since there are two diametricallyopposed contacts I3 which cooperate with the contact fingers. Thisconstruction is particularly advantageous as two contact fingers atopposite sides of the disk 25 may be set in positions corresponding toadjacent or closely adjacent channels. The two bridge pieces 21 are soarranged that one slot 21 has an angular extent of somewhat more than180, thus permitting the location of contact fingers over the full rangeof tuning adjustment of the gang condenser. As indicated at the leftside of Fig. 2, the center lines and therefore the operative positionsof two contact fingers I4 at opposite sides of the disk 25 may bedisplaced by an angle a which is less than the angular displacementwhich is possible between adjacent contact fingers.

As is shown in Figs. 4 and 7, the axial spacing of the disk 25 and thecontact-carrying plate I! is such that the contact fingers I4 do notengage the ends of the plate II or the contacts I3 when the cam plate 2Iis so adjusted that the contacts I5 engage the plate I6. With thisadjustment of the parts, the receiver may be tuned in the usual mannerover its full operating range. When the cam plate is adjusted to flexthe ends of the plate II away from the fixed end plate I6, the contactsI3 are moved outwardly into the path of the contact fingers I4, and theswitches I5, I6 are opened to include the resistor III in the cathodecircuit of the tube or tubes I. With this adjustment there will belittle or no output from the reproducer 5 unless the tuning condenser isset to some one of the pre-selected positions corresponding to anengagement of one of the contact fingers I4 with its cooperating contactI3.

As shown in Fig. 3, the flanged ends of the plate I! are centrallynotched and the edges are rounded to permit the ends of the fingers I4to ride smoothly up the edge and drop into the central notch as theshaft 6 is rotated. The contact I3 has a V-shaped notch to receive andaccurately center the tip of a finger I4 which drops into the notch ofthe plate II. The flexed tips of the resilient fingers provide areliable contact engagement with the contacts I3, thus avoiding thenoisy operation which would result from a contact of varying resistancein a biasing circuit. The notched construction of the contacts l3 andthe supporting plate I! provides an indexing action which facilitatestuning to the pre-selected favorite station. This indexing action doesnot take place, however, when the cam plate 2| is adjusted to engage thecontacts I5 with the plate I6.

As indicated above, the notched edges of the contacts I3 act as guidesto center the contact fingers I4 in one definite position, and theshapes of the notches in each contact I3 and the plate H are so relatedthat the cooperating contacts are in electrical engagement only when thefinger I4 is accurately centered in the groove. The receiver thereforetunes sharply to each of the pre-selected stations when the mutingsystem is used. By initially adjusting the contact fingers to positionscorresponding to accurate tuning to resonance at the desiredfrequencies, the operator is assured of accurate tuning, and thereforeof good quality reception, whenever a station is brought in by theautomatic muting switch system.

As shown in Fig. 9, the angular throw of the cam plate may be reduced byproviding a pair of cams 20 for cooperation with each end of the plateI'I, one cam of each pair entering a slot 21 in one end adjustment ofthe cams. The double cam construction has the further advantage that theplate I 1 is not warped transversely when the ends are flexed by forcingthe cams between the plate and the annular disk I8.

There is considerable latitude in the design. of the switch elements andFigs. 10-12 illustrate alternative constructions of the contact fingers.The contact portions of all contact fingers may be conveniently made ofidentical size and shape by riveting short sections 28 of extruded barmaterial to resilient fingers I411. The contacts 26 are preferablyof'brass, bronze or likematerials which may be readily extruded andwhich have good electrical propertieswhile the fingers I la may be ofspring steel. Another type of rounded contact tip 29 may be formed bystamping the. flared end of a contact finger Mb into U-shape.

While the double contacts I3 and [5 are preferably used toextend theadjustment range of the contact fingers and to obtain greaterreliability in the shorting of the muting resistor it when full rangetuning is desired, it will be apparent that some advantages of theinvention may be obtained when only one contact element l3, I5 isemployed. This and other changes which may be made in the electrical andphysical construction of embodiments of the invention fall within thespirit of my invention as set forth in the following claims.

I claim:

1. A radio receiver of the type including a tuning system, a switchsystem for rendering said receiver operative only when said tuningsystem is adjusted for the reception of signals of one of a pluraltiy ofpredetermined frequencies, said switch system including indexing meansproviding a mechanical indication of those settings of the tuning systemwhich correspond to adjustments to the p-re-selected frequencies, and amanually controlled switch for rendering said receiver operativethroughout the entire frequency range of said tuning system,characterized by the fact that means is provided torender said indexingmeans inoperative when said manually controlled switch is positioned forfull-range operation of said receiver.

2. A radio receiver as claimed in claim 1, wherein said, last means ismechanically connected to said manually controlled switch for operationsimultaneously therewith.

3. In a radio receiver, the combination with adjustable means for tuningthe receiver over a frequency range, a detector, a reproducer, and meansfor preventing the overall transmission of signals through said receiverand reproducer, of switch means for rendering saidtransmissionpreventing means inoperative, said switch means comprisingcooperating contact means in the form of a contact and a plurality ofcontact members, means connecting one of said contact means to saidadjustable tuning means for operation synchronously therewith, and meansfor displacing one of said means into and out of alternate positionswhich permit and which prevent, respectively, the engagement of saidcontact means during the movement of that contact means which isconnected to said adjustable tuning means.

4. A radio receiver as claimed in claim 3, wherein said plurality ofcontact members comprise that contact means which is mechanicallyconnected to said tuning means.

5. A radio receiver as claimed in claim 3, wherein said contactcomprises that means which is displaceable to prevent engagement of saidcontact means.

6. A radio receiver comprising a radio amplifier including rotatableadjustable means for tuning the same over a frequency range, the tuningmeans adjustment being complete within substantially 180 rotation of theadjustable means, a detector, at reproducer, and a muting system forcontrolling the overall transmission through the receiver, said mutingsystem including a contactcarrying member rotatable synchronously withthe adjustment of said tuning means, a plurality of contact fingersadjustably mounted on said member, and a pair of relatively fixedcontacts at opposite sides of the axis of rotation of said member, thesaid contact fingers being secured in positions on said member whichbring the same severally into engagement with one or the other of saidfixed contacts when said tuning means is adjusted to positionscorresponding to certain predetermined frequencies, said contact fingersbeing resilient and said fixed contacts are notched to provide anindexing action, in combination with means for simultaneously displacingboth of said fixed contacts to positions outside the path of movement ofsaid contact fingers.

'7. In a radio receiver of the automatic muting type, an amplifier andmeans for tuning the same over a frequency range, a detector workinginto an audio amplifier and reproducer, and means including a mutingswitch system for controlling the overall transmission of said receiver;said muting switch system comprising a relatively fixed contact-carryingmember of resilient material, a contact element secured to and insulatedfrom said member, a rotatable contact-carrying member, a plurality ofcontact members adjustably secured to said rotatable member, andmanually operated means for flexing said relatively fixed member to movesaid contact element into and out of the path of movement of saidcontact members.

8. A radio receiver as claimed in claim '7, in combination with a fixedmeans having the same electrical potential as said contact members, saidfixed means being positioned to be engaged by said contact element whenthe latter is positioned outside of the path of movement of said contactelements.

9. In a radio receiver, the combination with an adjustable tuningelement and a network having a pair of terminals which must beelectrically connected to place the receiver in operating condition, ofmeans for connecting the said terminals; said means comprising a diskmember rotatable synchronously with the adjustment of said tuningelement, a resilient plate having a flanged end located adjacent theperiphery of said disk member and with the flanged end substantiallyparallel to the axis about which said disk member may be rotated, acontact element secured to and insulated from said flanged end, aplurality of contacts mounted on said disk member for engagement withsaid contact element, said plate normally positioning said contactelement outside the path of movement of said contacts, and cam meansoperable to fiex the said plate to displace said contact element intothe path of movement of said contacts.

10. In a radio receiver of the muting type, a radio amplifier andadjustable means for tuning the same, a fixed plate, a shaft extendingthrough said plate and rotatable synchronously with the adjustment ofsaid tuning means, a disk on said shaft and carrying a plurality ofcontacts, a resilient member having a portion secured to said fixedplate and another portion carrying a contact element, and cam means forflexing said resilient member to move said contact element intoalternative positions for cooperation alternately with said contacts andwith said fixed plate to complete an electrical circuit.

11. A receiver as claimed in claim 10, wherein the range of adjustmentof said tuning member corresponds to a maximum angular adjustment ofsaid shaft of not more than 180, and said resilient member carries asecond contact element which is spaced from said first contact elementby an angle substantially equal to the said maximum angular adjustmentof said shaft.

12. A radio receiver comprising a tunable amplifler including anadjustable condenser assembly 5 having end plates and a shaft extendingbeyond both end plates, a disk member secured to a projecting end ofsaid shaft, a plurality of contacts adjustably secured to said diskmember, a resilient member secured to the end plate adjacent said 10disk member, contact means carried by and insulated from said resilientmember for cooperation with said contacts, and cam means for flexingsaid resilient member to displace said contact means into and out of thepath of movement of 5 said contacts.

13. A receiver as claimed in claim 12, wherein said resilient member hasa centrally apertured portion through which the said projecting end ofsaid shaft extends, and a pair of radially extend- 20 ing portions whichterminate in flanged ends, and said contact means comprises a contactelement secured to each of said flanged ends of the resilient member.

14. A radio receiver as claimed in claim 12,

wherein said contacts comprise resilient contact fingers.

15. A radio receiver as claimed in claim 12, wherein said contactscomprise resilient contact fingers having the contact ends thereof bentinto U-shape.

16. A radio receiver as claimed in claim 12, wherein said contactscomprise resilient contact fingers, and contact elements secured to saidfingers.

17. A radio receiver as claimed in claim 12, wherein said contactscomprise resilient contact fingers, and contact elements of extrudedmetal secured to said fingers.

18. A radio receiver as claimed in claim 9, wherein said resilient plateis apertured adjacent said flanged end, and said cam means comprises acam plate and a pair of cams thereon, one cam projecting through saidaperture and the other lying adjacent said resilient plate when said camplate is adjusted to position said contact element outside the path ofmovement of said contacts.

WILLIAM D. LOUGHLIN.

